Businessman Tim Burns (R) left the race to challenge Sen. Bob Casey (D-Pa.) today, citing lack of support from state GOP officials.

His departure signals Republicans are winnowing their crowded field of candidates ahead of the April 24 primary.

Over the past week, Gov. Tom Corbett (R) and the Pennsylvania State Committee endorsed businessman Steve Welch for the GOP nod. Burns suggested in a statement that this effectively ended his statewide campaign.

“When I began this process I put a premium on getting the endorsement of the Republican Party," Burns said. "Governor Corbett made a choice in this primary, and the State Committee has confirmed his choice."

Pennsylvania Republicans will have a tough time ensuring Casey does not win a second term. The Democrat had almost $4.4 million in the bank at the end of last year, and Roll Call rates the race as Likely Democratic.

Even after Burns' exit, the field remains varied and large. In addition to Welch, former coal company executive Tom Smith, attorney Marc Scaringi and former state Rep. Sam Rohrer are running for the GOP nomination.